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Magnetic field effects (MFEs) on the intramolecular exciplex fluorescence of a chain-linked phenanthrene (Phen)/N,N-dimethylaniline (DMA) system, Phen–(CH2)n–O–(CH2)2–DMA, have been studied in the magnetic fields (≤0.62 T) as functions of (1) solvent polarity (ε = 7.6—36.7), (2) chain length (n = 4—12), and (3) temperature (223—333 K). The MFEs on the exciplex fluorescence are attributable to the singlet–triplet intersystem crossing in the intramolecular radical ion pair which is in dynamic equilibrium with the exciplex. (1) Solvent polarity increases significantly the MFEs on the exciplex fluorescence of Phen–(CH2)10–O–(CH2)2–DMA. This is attributable to the stability of the intramolecular radical ion pair relative to the exciplex. (2) A remarkable influence of chain length on MFEs in the exciplex fluorescence in N,N-dimethylformamide (DMF) was observed. The results were discussed in connection with the edge-to-edge distances <r> of two radicals obtained from molecular dynamics calculation for model compounds. (3) The temperature-induced high-field shift of the exchange energies |2J| for Phen–(CH2)4–O–(CH2)2–DMA in DMF was discussed in connection with <r>.

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